Flash analyzer



May 20, 1952 JAFF'E 2,597,001

FLASH ANALYZER Filed June 9, 1945 2 sHEETs-sHEET 1 RECORD.

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MARKER M IXER MPLI smcn. sweep F CIRCUIT 22 {4A I INVENTOR.

BERNARD M. JAFFE ATTORNEY May 20, 1952 JAFFE 2,597,001

FLASH ANALYZER Filed June 9, 1945 2 SHEETSSHEET 2 FIG. 3

CANDLE POWER MAGNETIC TAPE IiIGI 4 W sweep I WAVE l H I lnjlll l l rAPERTURE I3 I I I /wz,

Sol 02 503 DIRECTION OF ROTATION 0F DRUM [2 AND OF SCANNING IN VEN TOR.

' Q MMQ ATTORNEY BY BERNARD M. JAFFE Patented May 20, 1952 STATES PATENT ore-E;

2,597,001 I FLASH ANALYZER Bernard M.-.Ja'ife,- NewzYork,,N; Y, Application June 9, 1945,;Serial No. 598,484

(o1. law-+352.)

2 Claims.

( Granted The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a flash azimuth locator, or a device capable of determining the azimuth of a distant, instantaneous flash, such as are visible with a naked eye at night, and with .the flash azimuth locator-inthe daytime. These flashes alone, or together with some additional apparatus not disclosed inthis application, may be used for determining either the azimuth alone or the exact location, i. e., both azimuth and range, of a flash-source. Since the location of guns by their flashes has beenpracticed-in the past and the enemy is always on guard against such contingency, there are occasions when the enemy resorts to setting off simulated gun flashes to. confuse the opponent. It has been discovered that efiective simulation of the real gun flashes is difficult, if the flashes are analyzed spectroscopically. An actual gun-flash will exhibit,.when viewed in .a .spectroscope, a line spectrum superimposed on acontinuous spectrum; the line spectrum isdue to the burning gases. and the continuous spectrum is due to incandescent carbon particles. Since it, is difiicult to simulate the line spectrum of the actual-gun flash by some artificial means, the simulated flashes may be detected and separated from the real gun-flashes by means of therecording flash spectrograph. I

It is therefore an object-of .thisinventionto provide a flash azimuth locator capable ofi-distinguishing the desired distant flashes from the simulated flashes in the process of determining the azimuth of the desired flashes by presenting the flashes in the form of characteristic line spectra. 7

Anadditional object of this invention is to provide a spectroscopic and collimator-system provided with instrumentalities for limiting the light entering the spectroscope to that which comes only from a source substantially alon the optical axis of the collimator soithat,onlywthe under the act of March 3, 1883, as amended April '30, 1928; 370 Q. G. 757) flashesalong theprev'iously determined azimuth j of the flashrmayliaveanyeffect on the flashazi- .muth recorder. l

mils. line joining the corners of the square aperture Stilllanotherobject of this invention is to pro vi-dea, spectrograph in which the optical axes of thecollimator and of the telescope are parallel.

These and other features of the invention will be moreclearly understood from the following .detailed description and the accompanying drawing in which,

Figure 1 is block diagram of the flash azimuth vlocator provided with a spectrograph,

Figure 2 is a plan view of the spectrograph .usedin connection with the locator.

it is desiredto examine, in the plane of rectangularaperture l3 providedin an, aperture plate 14.

Plate I4 is mounted directly in front of a scanning cylinder. [.2 which consists ofa slotted drum having. equidistant slots II. The scanning drum is mounted on a vertical shaft and scans the aperture. from one side-edge of the aperture to the .otherlwith the narrow vertical slots. In one embodiment of the invention, the horizontal slot dimension, .i. e., in the direction of scanning,

has anangular slot width of 1 mil since this is the desired limit of angular resolution of the locator. The optical axis of the telescope is coaxial with the normal axis of the aperture and is in the radial relationshiptc the cylinder. The aperture is the flcld stop of the system,and its size, together with the'constants'of the optical system, determine the angular field of View of the-instrument, which in a typical case is mils by It is preferable tomake the diagonal equal to the diameter oft the image of the field of view of the: telescope produced by. the latter in. the planecof aperture [3; this is done in order toutilize as much of the image as possible. Thus, the dimensions of the aperture depend upon the focal length of the lens system used in-the telescope and the-desired angle of acceptance of this lenssystem. :The light leaving theaperture .is

sufficientl -divergent so that a photo-electric cell I I5 placed immediately behind thedrum, receives asufilciently defocussed light to avoid complete obstruction of any image by the anode of the cell and the concomitant formation of the blind spots. Thev scanned gun flash is converted into electrical pulses which are impressed on a recording amplifier IS, the output of which is connected through a switch IT to a recording magnetic head H! which is positioned in recording-.-

relationship with respect to a magnetic tape I0. The distance between the center lines 420 and 42!, Fig. 4, of the scanning slots H is preferably equal to the horizontal dimension of the aperture, as illustrated in Fig. 4, where two scanning slits ll of scanning drum [2 are drawn so that their center lines coincide with the side-edges 422 and 423 of aperture l3. This is done to insure that the successive scanning cycles are continuous, without either excessive overlap or blank space, as illustrated at 400 through 403 in Fig. 4 where the cross-hatched portions illustrate'the signal due to general background illumination present in the field of view of the telescope I duced by flash'300, when its image in aperture I3 is scanned by slits I I. It may be noticed that in Fig. 4. the background illumination never-drops down to zero level indicated by a reference line 401, which is due to the fact that when the lagging edge of one slot leaves the aperture, the succeeding scanning slot is in full view of the aperture. This .being the case, there exists a slight overlap of the two successive slots and, as

a consequence, the photo-electric cell is never cut off completely from the aperture. Any excessive overlap of the two adjacent slots with the aperture must be avoided since it would result in con- '7 fusion and jumbling of information from two "parts of the field; blank spaces are not positively objectionable in that they do not result in the confusion of intelligence on the oscilloscope screen but they do limit or decrease the resolution of the total system'by decreasing the portion of the frame devoted to useful information.

' These slots in atypical case pass across the aperture, i. e'., scan the field of view, at a rate of not lessthan 100 times per second. The reason for this rate of scanning will become more apparent on later consideration of the characteristics of the flash,'and especially of its duration. Each scansion is in many respects equivalent to one frame of a motion picture film; the terminology of'this analogy will be used in several instances in this disclosure.

l2, and the-magnetic tape are placed on the same, vertical shaft 20 which is connected to a motor 2|. The tape is mounted concentric with and before the recorded signal is erased by the erasing head.

After the flash has been recorded on magnetic tape [9 and the erasing and reproducing heads disconnected, the recorded signal is viewed on the screen of an oscilloscope 25, the vertical deflection plates of which are connected through mixer 26 and a reproducing amplifier 2'! to reproducing heads 28 and 29, which are connected in series :through a switch 30, which is in its upper position during this portion of the reproducing cycle. but in phase-opposition for eliminating the extraneous background illuminations which may I bealso present as an additional recorded signal while 404, 405, and 406 are the light signals pro- The scanning .slotted drumand rigidly attached either to the upper or lower edge of the periphery of the scanning drum, the

two being rigidly connected to shaft 20 so that they are rotated at the same speed by motor 2|. An oscillator 22. is connected through a switch the magnetic tape in front of the recording head. Switches I! and 23 are ganged switches which are opened by the operator immediately after the observation of the flash with the result that the record of the flash is retained on magnetic 23 to an erasing head 24 which is positioned on driven by the motor at l revolution per second.

This time reservoir is ample for allowing the operator to disconnect the recording and erasing heads after observing the occurrence of the flash on the magnetic tape. This background signal is illustrated at 400 through 403. The reproducing heads 28 and 29 are spaced with respect to each other,- along the magnetic tape so that while the first head 28 isplaying back the background signal 400 plus the recorded pulse 404, the other head is playing back the signal due to the background noise 403 alone. The pick-up heads are adjusted to have the same sensitivity so that if the background signal has not changed appreciably during the short time interval required for the tape to travel from the first to the second pick-up head, the background signal is cancelled out and only the signals 404, 405, and 506 due to the gun flash are impressed on the reproducing amplifier 2'! and the vertical deflection plates of oscilloscope 25. The two pick-up heads are preferably placed at least 3 frames apart and the scanning cylinder is driven at such a rate that the duration of a typical gun flash shallbe scanned in'3 frames, as is disclosed more fully in connection with Fig. 4. The obliterating, recording and pick-up heads are all mounted on a base plate which itself is mounted independently of the scanning disc I2 on a tripod supporting the flash azimuth locator. The reproducing heads 28 and 29 are provided with the mechanical means for shifting their position with respect to the magnetic tape during the preliminary adjustment of the locator which results in shifting of the reproduced signal on the screen of oscilloscope 25 with respect to the marker signals or scale gratings 27 also appearing on the same screen. Once this adjustment has been accomplished, the heads are locked inthe desired position, and remain stationary from then on.. The sweep circuit 32 of the oscilloscope is synchronized by means of a commutator 3| mounted on shaft 20 and a commutator brush 33 with the scanning of the aperture by slots ll so that a saw-tooth '4l0, Fig. 4 voltage is generated once during each scanning period in which slot ll scans aperture |3.- Mixer 26 is also connected to a reference marker amplifier 34 which is connected to a synchronizing brush 35, and a commutator 36 connected through step-up ratio gears 31 and 38 to shaft 20 and motor 2|.

For an understanding of the rate of scanning and synchronization reference is made to Figs. 3 and 4. In Fig. 3 the illustrated curve 300 represents the intensity-of-flash-vS.-time curve of a typical gun flash. The gun flash lasts for approximately 0.03 second and may be of the order of 100,000 candle power. In Fig. 4, [9 represents the magnetic tape with the reproducing heads 28 and 29 placed in the proper position with respect to the tape. The irregular cross-hatched curves 400 through 403 represent the signals'recorded on tape [9 due to the light intensity of the backround or the previously mentioned background signal, and 404, 405, and 406 represent the superimposed flash signals also "recorded on the tape.

The first portion 404" of the recorded'flash happened to coincide with the maximum candlepower of I flash 300' while the remaining portions 405 and 4&0 reproduce the lower intensities of the flash. It is desirable to have the flash scanned with at least three slots to avoid missing the flash altogether or reproducing only the weaker'portions of thejilluminati-on.. When threeslots scan the flash, the' scansions being one second apart, one of them is bound to coincide with a fairly high intensity of illumination on-the curve, which is apparent from the examination of Figs. 39nd 'sitivities, or reasonably so, "there-will be substantially complete cancellation'ofthe background signal with the result that only theflash'signals 404, 405 and 408 will be reproduced as an image 39 on the oscilloscope screen in a manner illustratedin Fig. l. The linear portion of thesawtooth voltage j4|0 has approximately the same period as the timerequired for scanning withone slot, i. e., 0.01 second. '11? it is desired to scan 3 frames per flash, the-scanning cylinder may have 100 evenly spaced. slots ll andbe driven at 1 revolution per second. Fig. lalso illustrates, with the aid of the vertical dotted lines, the synchronization of the magnetic tape, sweep voltage, and the-instantaneous position of slots I with respect to aperture [3;and arrow 41-2 and 4 l3 indicate-the direction of rotation of drum [2 and tape 19.

which during the recording cycle corresponds to' the instant when the lagging edge of slit ll reaches the side-edge 422 .or 423 of aperture I3.

At this instant the sweep-controlling brush 33 leaves the shorting segment on commutator 3l,, 0

this shorting segment dischargingthe saw-tooth generating condenser in the interim of time required for slit l I to travel 0.5 mil across-aperture l3, 1. e., half of the slits Width. When the synchronizationof the reproduction and of the sawtooth generator isas described above, the position of pulse 319 on the oscilloscope screen depends upon the azimuth of the flash since the azimuth of the flash determines the position of its images 404, 405, and 406 within aperture l3, and the re-. maining apparatus, 7 because of the illustrated timing of the saw-tooth wave 4l0 with respcet to tape l9, and especially thesignals recorded on the tape with the aid of thescanning slots H, simply 4. If the duration of the gun-flash is in'the order I transfers the images of the flash produced at the aperture onto the oscilloscopescreen. Thus the azimuth of the flash determines the position of image 39 on the oscilloscope screen and saw-tooth wave 4I0 acts as a timing locus for positioning this image in proper azimuth relationship on the,

' ends of the sweep line onthescreen' representing the edges 422 and 423 cf aperture I 3 After the azimuth of the-recorded flash has been determined in accordance with the described procedure, the optical axis '9 of the locatoris rotated, if necessary, so'as to point it directly at the source of flash by-turning the-locator on its vertical axis-secured tothe tripod an angle equal to'the previously determined'azimuth angle. With such orientation of the azimuth 10- cator with respect to the source of flash, the next succeeding flash from the same source would be reproduced directly in the center of the screenof rectly at the source of'flash, telescope l0'is swung, with the aid of bracket 42', away from'its-nor'mal position which is in line with the optical axis of the locator, and spectrograph 40 is swung into the position previously occupied by telescope 10 so that the opticaliaxis 43 of the image-forming lens, or telescope, of the spectrograph now coincides with the position previously occupied by the optical axis '9 of the telescope. Thusthe next flash, coming from the same source, will be intercepted by the same flash azimuth'locator' in which its telescope ID has been replaced by spec'- trograph 40, and as a result' the flash signal recorded on the same magnetic tape 19 will include a signal produced by the incandescent carbon particles and a series of signals due to the line spectrum of the flash. The spectrum is produced by the burning gases causing the flash. Fox Viewing the signals recorded on the magnetic tape, switch 30 is used in its lower position so that only reproducing head 28 picks up the signals from the magnetic tape. Since the spectral'iin'agescompletely embrace the entire field of view, the background noise is substantially eliminated by the received gun flash and therefore the use of background noise eliminating head 29 is not required. The signal that'appears on the oscilloscope'screen is illustrated in Fig. 5; it consists of an approximately uniformly illuminated field 5'00 and a seriesofspectral'lines50l, 502, and 503 whic'h are used for identifying the flash and for determining whether it isa true gun flash or a simulated flash.

Since the simulated flash willhave different spectral distribution as compared to the spectral distribution of the true flash, comparison of the outline illustrated in Fig. 5with the known outline of the true gun flash will-identify the nature of the intercepted flash. If the two match each other, the recorded flash is the true gun flash. When this is not the case, the recorded flash is a simulated flash.

Fig. 2 discloses the spectrograph'on a magnified scale. It consists of an image-forming telescope illustrated diagrammatically as a lens 202 which is positioned in front of "an aperture plate 200 provided with an aperture 20 l'. The image of the flash is produced in the plane of aperture 20l and is then intercepted by a collimator 204 which converts the intercepted beam of light 2E0 into a parallel beam of light205. This isintercepted by a mirror 206 which deflects beam 205 so that it enters a light-resolving prism 20'! which resolves the light into the'individual wave length components 2E8, 209, 2l0, etc. These are intercepted by an image-forming telescope illustrated'as'a condenser, lens 2 |2Iwhich forms an image 214 of the spectrum at aperture l3" and it is this spec- 7 trum that is scanned by disc l2 and photo-electric cell l5. The spectrograph is provided with aperture 20! and aperture member 290 so that only the source of light directly in line with the optical axis 9 of the locatormayhave any effect on the photo-electric cell, the side flashes, such as flashes 2l6 and 2, having no effect on the scanning system since all illumination produced by these flashes is intercepted by the aperture member 290, as illustrated in the figure. The light-reflecting mirror 206' is mounted on a bracket'2l8, and the bracket is supported by a round pin 220; the pin in turn is supported by an outer casing 222 of. the spectrograph. The axis of pin 220 is parallel to edges 224, 225, and 226 of the prism, and the plane of mirror 206 is parallel to the axis of pin 220. The purpose of mirror 206 is for making the optical axis 228 of telescope 202 and collimator 204 parallel to the optical axis 230 of telescope 2E2. Accordingly the angular position of the mirror with respect to the beamof light 205 is dictated by this parallel relationship of the two optical axes. The light-reflecting mirror 206 is placed between the collimator lens 204 and prism 20?. The parallel relationship of the optical axes 228 and 230 may be also accomplished by placing mirror 296 between prism 20! and telescope 212, as illustrated in Fig. 1, where spectrograph 49 is constructed with the reflecting mirror placed between the prism and the spectrumfocussing telescope.

The invention thus discloses an azimuth locator provided with two optical systems, one being telescope l9, and the other spectrograph 40, telescope I9 is used for pointing optical axis of the azimuth locator directly at the source of flash While spectrograph 49 is used for producing the spectrum of a subsequent flash from the same source. The spectrum is recorded on a magnetic tape and is reproducedduring the reproducing cycle of the system as a series of spectral lines SOL-593. These are compared with the known spectrum of a real gun flash, this comparison revealing the fact whether the recorded flashes are real flashes or simulated flashes. I

The spectrograph provided for obtaining the aforementioned results includes aperture plate 209 for restricting the field of View of the spectrograph to a very small angle of acceptance so that the side flashes. or background illumination haveno appreciable effect on the flash azimuth locator. The spectrograph is also provided with a reflecting mirror for changing within the spectrograph, the direction of the intercepted light so as to make the optical axis of. condenser 202 parallel to the optical axis of condenser 2l2. This is necessary for pointing the spectrograph directly at the object producing the flash subsequent to pointing the optical axis of the azimuth locator directly at the desired object. By making the two optical axes of the spectrograph parallel, it becomes possible to point the spectrograph in the desired direction by merely rotating it on bracket 42. Rotation of bracket 42 aligns the optical axis 230 of the telescope with the optical axis 9 of the azimuth locator and since the optical axis 228 oi telescope 202 is made parallel to the optical axes 230 and 9, the telescope lens 292 will be pointing directly at the object producing the flashes under investigation.

It is believed that the construction and operation of. the flash azimuth locator and spectrograph disclosed in this specification, as well as the advantages thereof, will be apparent from the foregoing description. It should -be.understood therefore that .while the invention has been illustrated and described several preferred forms, reasonable changes and modificationsmay be made by those skilled inthe'art without-departing from the spirit of the inven tion as sought to be defined in the following claims.

Iclaim:

1. A real gun flash detector comprising means to resolve a 'fiash into its spectrum, periodic means to scan said spectrum, a magnetic tape recorder to record the scanned spectrum, a reproducing head associated with said recorder to transduce said magnetic record into voltage variations, a cathode ray oscilloscope having beam control means, means to generate a sweep control voltage in synchronism with said periodic means, means to impress said sweep control voltage upon said beam control means to deflect said beam along a time base axis, and

means to impress the output of said reproducing head upon said beam control and to thereby deflect said beam along another axis.

cathode ray oscilloscope having beam deflection means, means to generatea sweep voltage in synchronism with said periodic scan means, means to impress said sweep voltage'upon said I beam deflection means to deflect said beam along a time base axis, and means to impress said reproducing head output upon said beam deflection means to deflect said beam along another axis.

" BERNARD -M. JAFFE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1.007346 Fery Oct.'31,-l911 1,727,173 Muller Sept. 3, 1929 1,921,630 Mechau Aug. 8, 1933 1,962,366 Skala June 12, 1934 2,039,355 Ts'cherm-ak 'May 5, 1936 2,193,606 Ulrey Mar. 12, 1940 2,378,383 Arndt June 19,1945 2,403,997 Potter July 16,; 1946 2,406,318 Brace Aug; 27, 1946 2,418,136 Munson et al Apr. 1, 1947 2,425,003 Potter -2 Aug. 5, 1947 FOREIGN PATENTS Number Country Date 15,493 Great Britain of 1900 683,656 Germany Nov. 11, 1939 873,671 France Mar. 30, 1942 OTHER REFERENCES Co., New York, NewYork, chapter 4, pages 109- lllinc. (CopyinDivision7.) s 

